Kabul -- - President Hamid Karzai of Afghanistan has been engaged in secret contacts with the Taliban about reaching a peace agreement without the involvement of his U.S. and Western allies, further corroding already strained relations with the United States.

The secret contacts appear to help explain a string of actions by Karzai that seem intended to antagonize his U.S. backers, Western and Afghan officials said. In recent weeks, Karzai has continued to refuse to sign a long-term security agreement with Washington that he negotiated, insisted on releasing hardened Taliban militants from prison and distributed distorted evidence of what he called U.S. war crimes.

The clandestine contacts with the Taliban have borne little fruit, according to people who have been told about them. But they have helped undermine the remaining confidence between the United States and Karzai, making the already messy endgame of the Afghan conflict even more volatile.

Support for the war effort in Congress has deteriorated sharply, and U.S. officials say they are uncertain whether they can maintain even minimal security cooperation with Karzai's government or its successor after coming elections.

Frustrated by Karzai's refusal to sign the security agreement, which would clear the way for U.S. troops to stay on for training and counterterrorism work after the end of the year, President Obama has summoned his top commanders to the White House for a meeting on Tuesday to consider the future of the U.S. mission in Afghanistan.

Western and Afghan officials, who spoke on the condition of anonymity because of the private nature of the peace contacts, said that the outreach was apparently initiated by the Taliban in November, a time of deepening mistrust between Karzai and his allies. Karzai seemed to jump at what he believed was a chance to achieve what the Americans were unwilling or unable to do, and reach a deal to end the conflict - a belief that few in his camp shared.

The peace contacts, though, have yielded no tangible agreement, nor even progressed as far as opening negotiations for one. And it is not clear whether the Taliban ever intended to seriously pursue negotiations, or were simply trying to derail the security agreement.